This invention relates to a process for the production of polyurethanes in which ketene acetals containing dialkylamino groups are used as catalysts.
Polyurethanes having a variety of physical properties have long been produced on an industrial scale by the isocyanate-polyaddition process from compounds containing several active hydrogen atoms, more particularly compounds containing hydroxyl and/or carboxyl groups, and polyisocyanates, optionally in the presence of water and/or organic blowing agents, catalysts, emulsifiers and other additives (Angew. Chem. A 59 (1947), page 257).
By suitably selecting the reaction components, it is possible to produce homogeneous or cellular products, elastic and rigid foams as well as materials between those extremes.
Polyurethane foams are preferably produced by mixing liquid components. The starting materials to be reacted with one another may be mixed at the same time or an NCO preadduct may first be prepared with polyols and then foamed.
Tertiary amines have been successfully used as catalysts in the production of polyurethane foams because they are capable of accelerating both the reaction between hydroxyl and/or carboxyl groups and the NCO-groups and also the reaction between water and the isocyanate groups. In a one-shot process, the reactions taking place simultaneously can be coordinated. In addition, the foaming process is accompanied by additional crosslinking reactions in which allophanate, biuret and cyanurate structures are formed. In view of the complexity of the reactions involved, it is necessary to ensure that they take place synchronously by selecting the appropriate catalyst to make certain that the catalyst is not prematurely fixed in the foam through incorporation and does not adversely affect the hydrolytic degradation of the finished foam at a later stage. The odor of many of the tertiary amines commonly used is not however compatible with their application in foams.